Carboxylesterases play an important role in the metabolism and disposition of many clinically used medications including angiotensin-converting enzyme inhibitors, anticancer agents, statins, central nervous system stimulants, and drugs of abuse such as cocaine and heroin. The major human carboxylesterases, hCE1 and hCE2, are highly expressed in the liver and intestine, respectively, where they participate in two reactions important for drug metabolism - the conversion of ester prodrugs to active metabolites and the hydrolysis of active drugs to inactive moieties. Therefore, inhibition of the catalytic activity of carboxylesterases could significantly alter the disposition, therapeutic efficacy, and toxicity of substrate drugs. Drug interactions involving inhibition of cytochrome P450 enzymes are well known causes of adverse drug events. In distinct contrast, little information is available on whether drug interactions are important for carboxylesterase substrate drugs. Recent evidence from an animal model suggests that ethanol is a potent inhibitor of carboxylesterase- mediated first-pass drug metabolism, but important questions remain about the mechanisms of this interaction and the applicability to humans. Our long-term goal is to characterize in vivo factors affecting the disposition and response to carboxylesterase substrate drugs. The goal of this application is to translate the findings in animals to humans and characterize the in vivo mechanisms of this interaction. The overall hypothesis is that ethanol reduces first-pass metabolism of oral carboxylesterase-substrate drugs by inhibiting both hCE1 and hCE2. To test this hypothesis, probe drugs specific for each enzyme will be administered with and without ethanol to healthy human volunteers in an open label, randomized, crossover design. The specific aims are to: 1) determine the effects of ethanol on the pharmacokinetics of the hCE1 substrate drug oseltamivir;and 2) determine the effects of ethanol on the pharmacokinetics of the hCE2 substrate drug aspirin. With over 100 million people in the United States consuming ethanol and the growing number of drugs dependent on hydrolysis by carboxylesterases, recognition of these enzymes as potential targets for metabolic inhibition by drug interactions has the potential to improve the safe and effective use of this widely prescribed class of medications. PUBLIC HEALTH RELEVANCE: The inhibition of the carboxylesterase enzymes by ethanol could alter the effectiveness of many important drugs. Understanding this interaction is a necessary component for the safe and effective use of drugs metabolized by carboxylesterases. !